In a conventional technology described in Patent Literature 1, a power factor improvement circuit that improves a power factor of a power supply to reduce a harmonic component included in an input current is disclosed. A full-wave rectification mode or a voltage doubler rectification mode is selected and a short-circuiting start time and a short-circuiting time in a short-circuit element are controlled by an open-loop, whereby a power factor improvement function and a boosting function are obtained. That is, in the conventional technology of Patent Literature 1, a switch for switching a rectifier circuit is turned on/off to control a rectifier circuit into the full-wave rectification mode or the voltage doubler rectification mode, thereby roughly classifying a DC output voltage of the power factor improvement circuit into two stages. A short-circuit variable control on the short-circuit element in the open-loop further classifies the regions provided by these two stages into two stages, the one providing no improvement in the power factor and the other improving the power factor, such that a DC output voltage region has four stages as a whole. This improves the power factor on a high load-side while increasing an output range of the DC output voltage.
In a conventional technology described in Patent Literature 2, there is provided a DC voltage control unit that outputs a DC voltage control signal in correspondence to a deviation value between a DC output voltage reference value, which is set in correspondence to a load, and a voltage between terminals of a smoothing capacitor. There is also provided a current reference calculation unit that outputs a current reference signal based on the product of a control signal from the DC voltage control unit and a sine wave-shaped synchronous signal synchronized with an AC power supply. On/off control on a switch element is performed at high frequency by comparison between this current reference signal and an AC-side current of a rectification element, and thus a DC output voltage is controlled into a desired value while an AC input current is controlled to have a sine wave-shape. As a result, it is possible to set a power factor of a power supply to 1 and reduce generation of harmonics.